1. Field of the Invention
The present invention relates to position sensors and more particularly to the digital representation of position with the utilization of fiber optic techniques.
2. Background of the Invention
Devices in the prior art for obtaining digital representation of angular rotation or linear displacement generally comprise transducers containing a coded pattern of conducting a non-conducting areas. Brushes in contact with this transducer will generate a one when in a conducting area and a zero when in a non-conducting area. These devices require complete electrical circuits for each bit in a generated code. Positional sensitivity for these systems is a function of the number of bits in the code, which in turn is limited by the size of the brushes. Increased sensitivity may be provided by utilizing a photoelectric encoder which comprises a disk with a multiplicity of concentric bands, or a multiplicity of parallel bands arranged in a rectangular fashion, wherein each band is divided into transparent and opaque segments. A light source is positioned on one side of the disk and photodetectors, or optical fibers leading to photodetectors, are arranged on the other side to position one photodetector, or optical fiber, in each band. When a transparent segment in a band is between the light source and the photodetector for that band, an electrical signal representative of a one will appear at the output terminal of the photodetector, and when an opaque segment is between the light source and the photodetector, an electrical signal representative of a zero will appear at the output terminal. This system requires as many detectors or optical fiber-detector combinations as there are bits in the coded signal. Both the electrical and optical systems require a multiplicity of data lines, as many as the number of data bits, to transmit the digital data to the processor. The present invention provides an optical analog-to-digital converter with which digital data is transmitted to a processor along a single, optical fiber without the necessity of providing electrical or optical energy at the encoder.